Methods for the Identification of the Three Major Eruptions from the Toba Complex, Indonesia

Tephra provide a valuable tool for palaeoenvironmental reconstructions when correctly identified. Here we present three approaches to discriminate between the Oldest, Middle and Younger Toba Tuff (OTT, MTT and YTT, respectively), these being three major Quaternary eruptions of the Toba volcano in Sumatra, Indonesia. Toba ash forms an important stratigraphic marker across peninsular India, and it has been widely used for archaeological and palaeoenvironmental studies. Major element ratios in YTT show post-depositional diagenetic effects from ash-environment interaction. Na2O/K2O varies up to 50% between marine and terrestrial sites, because of seawater induced alkali migration and site-specific water pH. However, major elements cannot discriminate between OTT and YTT, but these can be identified using trace elements data. Compiling several hundreds analyses of selected rare elements, four …